Ultrasensitive determinations of ATP were developed specifically to investigate the growth potential and functional biomass of host grown and "host dependent" microbes. The data represent the energy status in incubated type 1 (host grown) cells during the physiological eclipse, the time for type 11 (in vitro adapted) cells to generate energy at the rates used during growth in animal hosts and thereafter to quantitate the expansions of bacterial biomass. Mycobacterium lepraemurium (agent of rat leprosy and for 69 years a famous "obligate intracellular parasite") initiates genuine growth in Nakamura's (1972) system and serves as an interim model for Mycobacterium leprae and other "host dependent organisms." A series of physiological and nutritional deficiencies. OBJECTIVES: To use M. lepraemurium cells under controlled oxidation reduction potentials while: 1. Defining conditions and factors that greatly reduce the profound physiologic eclipse of Type 1 (in vivo grown) cells and, thus, to facilitate the fabrication of type 11 (in vitro adpated, growth competent) cells. 2. Defining and correcting the cause of cessation of growth after 6 weeks. 3. Checking the significance of evident progress by raising the incubation temperature and, as soon as progress warrants, by trials with M. leprae.